Styrene polymer composition containing butyl stearate and a metal compound



United States Patent Ofifice 3,057,813 Patented Oct. 9, 1962 STYRENEPOLYMER COMPOSITION CONTAIN- ING BUTYL STEARATE AND A METAL COM- POUNDRussell H. Fay, Midland, Mich., assignor to The Dow Chemical Company,Midland, Mich., a corporation of Delaware No Drawing. Filed Sept. 24,1956, Ser. No. 611,752

8 Claims. (Cl. 26031.2)

This invention relates to a discoloration-inhibiting treatment for butylstearate and like fatty acid esters which are commonly employed asinternal lubricants for polymeric compositions, particularly polystyreneand the like, to facilitate their fabrication during extrusion, moldingand similar operations. It has particular reference to polymericcompositions in which the treated ester lubricant is incorporated.

Although butyl stearate and like fatty acid esters are extremelybeneficial internal lubricants for polystyrene and similar polymericcompositions, they frequently tend to decompose at elevatedtemperatures, particularly in the presence of certain ferrous metalssuch as mild steel,

and cause discoloration in the polymeric composition. The discolorationusually occurs in the form of objectionable black specks which arebelieved to consist predominantly of the degraded free fatty acid, suchas stearic acid, from the ester. The conditions which seem to promotediscoloration of the butyl stearate are ordinarily present duringfabrication of polymeric compositions which are commonly extruded ormolded at elevated temperatures, frequently in the presence of suchdeleterious, discoloration-promoting ferrous alloys as mild steel.

It would be advantageous if butyl stearate and like fatty acid esterscould be employed as lubricants in polymeric compositions withoutoccasioning the discoloration that may occur from the decomposition ofthe ester lubricant when the composition is exposed to heat at elevatedtemperatures, especially when the exposure occurs in the presence ofmild steel and the like ferrous metal alloys.

To the accomplishment of this and related ends, butyl stearate and likefatty acid esters may be treated to overcome their tendency to decomposeand cause discoloration at elevated temperatures by incorporating in theester lubricant a minor proportion of a compound selected from the groupconsisting of the sulfites, sulfates, oxides and hydroxides of the groupI}, and II, metals of the periodic system and aluminum. The metalcompound that is incorporated in the ester lubricant saponifies orneutralizes the free fatty acid that forms upon its thermaldecomposition and prevents the discoloration that may occur when thefatty acids, such as stearic acid, are permitted to remain in a freeacid form. The treated fatty acid ester lubricant may be handled andincorporated in polymeric compositions according to conventionaltechniques, taking care that the metal compound is uniformly dispersedthroughout the fatty acid ester. Polymeric compositions, particularlypolystyrene, that are lubricated internally with fatty acid esters,particularly butyl stearate, treated in accordance with the presentinvention, are not discolored or contaminated with black specks due todecomposition of the fatty acid ester even when they are exposed to heatat elevated extrusion or molding temperatures in the presence of mildsteel alloys. Further, the metal salts of the fatty acids that areformed do not exert an undesirable influence on the composition. To thecontrary, they frequently contribute beneficial lubricatingcharacteristics of their own.

Ordinarily, the fatty acid esters may be suitably treated by theincorporation of less than a stoichiometric quantity of the metalcompound, based on the weight of the treated ester. In most cases,satisfactory results may be achieved when between about 10 and 25percent by weight of a stoichiometric quantity of the metal compound isemployed. Preferably, calcium hydroxide is utilized as the basic metalcompound for treating the fatty acid ester lubricant although it is alsoadvantageous to employ the oxides and hydroxides of the other alkalineearth metals, barium and strontium. Excellent results may also beobtained with the oxides and hydroxides of the alkali metals such assodium and potassium and aluminum hydroxide.

By way of further illustration, about 20 percent by weight of thestoichiometric equivalent quantities of several metal compounds fortreating butyl stearate in accordance with the invention Were separatelyadded to 200 milliliter samples of butyl stearate in sealed, evacuatedglass cylinders. Each of the samples was maintained at a temperature ofabout 240 C. for four days, after which they were observed for evidenceof discoloration. The treating compounds that were employed and theresults that were obtained are set forth in the following tabulation.

Treating Compound Results Remarks Calcium hydroxide.-. No discolorationExcellent. Calcium sulfate No discoloration-about 20 per- Good.

cent creamy white solid, remainder pale yellow liquid. Magnesium oxideNo diseolorationercamy white Do. solid formed. Sodium sulfite Veryslight darkening-mo black Satisfactory.

speck formation-about 5 percent white solid, remainder yellow liquid.Sodium sulfate ..do Do. Aluminum hydroxide. N0 discolorationvery littleExcellent.

white solid, remainder pale yellow liquid. Aluminum oxide Very slightdarkeningno solid, Suitable.

relatively dark yellow liquid. Zinc oxide About 25 percent solidremain-Poor.

der dark liquid.

Analogous results were obtained when the refluxing was conducted in thepresence of mild steel. In contrast, plain butyl stearate tested in thesame manner in glass discolored to an intolerable degree within a day.This effect was noted in much less than a day when the plain untreatedester was refluxed in the presence of mild steel. Polystyrene thatcontains butyl stearate as an internal lubricant which is treated inaccordance with the invention, especially with calcium hydroxide,magnesium' oxide, aluminum hydroxide and the indicated alkali metalcompounds, does not develop black specks or other color impurities evenwhen it is passed through a mild steel devolatilizing extruder atelevated extruding temperatures.

What is claimed is:

1. A styrene polymer composition containing butyl stearate as aninternal lubricant which has incorporated therein a metal compoundselected from the group consisting of the sulfites, sulfates, oxides andhydroxides of the group I, and II metals of the periodic system andaluminum, in a proportion up to about a stoichiometric quantity forneutralization of the free fatty acid available from the butyl stearate,based on the quantity of butyl stearate in the composition.

2. The polymeric composition of claim 1, wherein the butyl stearatecontains an amount of the metal compound that is between about 10 and 25percent by weight of a stoichiometric quantity for neutralization of thefree fatty acid available from the butyl stearate, based on the weightof the butyl stearate in the composition.

3. The composition of claim 1, wherein the metal compound is a calciumhydroxide.

4. The composition of claim 1, wherein the metal compound is a sodiumhydroxide.

5. The composition of claim 1, wherein the metal compound is a potassiumhydroxide.

6. The composition of claim 1, wherein the metal compound is a magnesiumhydroxide.

7. The composition of claim 1, wherein the metal compound is an aluminumhydroxide.

8. The composition of claim 2 wherein the styrene polymer ispolystyrene.

References Cited in the file of this patent UNITED STATES PATENTS OTHERREFERENCES Condensed Chemical Dictionary, 5th Edition, Reinholdublishing Co., New York, N.Y., page 966.

UNITED STATES. PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3,057,813 October 9, 1962 Russell H. Fay

It is hereby certified that error appears in the above numbered patentrequiring correction and that the said Letters Patent should read ascorrected below.

Column 3, line 11,

for the claim ref 11 read l erence numeral 2 Signed and sealed this 14thday of May 1963,

(SEAL) Attest:

ERNEST w. SWIDER DAVID LADD Attesting Officer Commissioner of Patents

1. A STYRENE POLYMER COMPOSITION CONTAINING BUTYL STEARATE AS ANINTERNAL LUBRICANT WHICH HAS INCORPORATED THEREIN A METAL COMPOUNDSELECTED FROM THE GROUP CONSISTING OF THE SULFITES, SULFATES, OXIDES ANDHYDROXIDES OF THE GROUP IA AND IIA METALS OF THE PERIODIC SYSTEM ANDALUMINUM, IN A PROPORTION UP TO ABOUT A STOICHIOMETRIC QUANTITY FORNEUTRALIZATION OF THE FREE FATTY ACID AVAILABLE FROM THE BUTYL STEARATE,BASED ON THE QUANTITY OF BUTYL STEARATE IN THE COMPOSITION.